Abstract
Possibly, the greater availability of nutrients in the soil will promote a more pronounced modification of the growth form of forage plant under high frequency of defoliation. To test this hypothesis, we characterized the changes in the growth form of Brachiaria brizantha cv. Marandu syn. Urochloa brizantha cv. Marandu (marandu palisade grass) submitted to cutting intervals and fertilization, as well as the effect of these modifications on the forages removed and remnant from the cut. This study was carried out in two experimental periods. In each period, independent yet similar in nature experiments were performed. In Experiment 1, from October 2013 to February 2014, marandu palisade grass was fertilized with 70 kg.ha-1 of N and 50 kg.ha-1 of P2O5 and cut intervals (7, 14, 28, 56, and 112 days) were evaluated in a randomized complete block design with four replications. In Experiment 2, from November 2014 to March 2015, in addition to the same cut intervals evaluated in Experiment 1, two fertilization conditions were also studied, one of which was low (50 kg.ha-1 of P2O5 and 75 kg.ha-1 of N) and another one that was high (100 kg.ha-1 of P2O5 and 300 kg.ha-1 of N). In Experiment 2, a factorial scheme with two levels of fertilization and five levels of cut intervals was used in a randomized block design with four replications. In Experiment 1, the highest indexes of horizontality (IH) occurred (p<0.05) in the plants under cut intervals of 7, 14 and 28 days, in relation to the plants cut every 56 and 112 days. In Experiment 2, only the plant cut every 7 days showed an increase of IH (from 1.3 to 1.5) (p<0.05) with the improvement of the high fertilization condition. The remaining forage mass increased (p<0.05) with the cut interval, from 412 to 483 g.m-2 and from 412 to 571 g.m-2 in Experiments 1 and 2, respectively. In Experiment 2, there was an increase (p<0.05) in the remaining forage mass (from 447 to 505 g.m-2) and the percentage of live stem (from 23 to 33%) with fertilization at all cut intervals. In both experiments, the highest cut intervals increased (p<0.05) the forage mass removed (from 95 to 840 g.m-2 and from 44.8 to 843 g.m-2 in experiments 1 and 2, respectively) and leaf area index (LAI) removed (from 1.0 to 4.3 and from 0.4 to 3.9 in experiments 1 and 2, respectively). In Experiment 2, the improved fertilization condition resulted in an increase (p<0.05) in the forage mass removed (from 261.3 to 391.8 g.m-2) and LAI removed (from 1.6 to 2.1). In Experiment 2, when the fertilization condition was high, there was (p<0.05) less percentage of live leaf removed in the canopies under intermediate cuts (28 and 56 days). When defoliation is very frequent, the greater availability of nutrients in the soil contributes to the marandu palisade grass to modify its form of growth from upright to prostrate, compared to the condition of less availability of nutrients in the soil. Increasing the cut interval and fertilization improved the forage removal of marandu grass.
Keywords:
Brachiaria brizantha; fertilization; nitrogen; phenotypic plasticity; phosphorus; Urochloa brizantha
